couldn’t he also change into lower gears and put in park as a last resort?
He could certainly put it in neutral, and coast to a stop. It wouldn't actually go into "Park", it would just grind against the "Park" pawl until the car stopped.
I'm assuming he was somehow stuck with some sort of condition keeping the throttle open. It could maybe have been a stuck cruise control, or a stuck throttle. Otherwise he could just let up on the foot control, and it would also coast to a stop. Putting it in neutral certainly beats ramming a police car, even if the engine is ruined from over revving.
He had lots of options (in this order): let up on the gas, turn off the key, put it in neutral, step on the brakes (and hold it hard until the car stops, so the brakes don't overheat).